of the cell-bodies to divide and the
consequent development of four spermatozoa in one cell.

Stenopelmatus.

The spermatogonium of _Stenopelmatus_ contains from one to three large
nucleoli, which stain much less with thionin than does the spireme
(plate II, figs. 46, 47, 48). As the distinct chromosomes come into view
in the prophase of mitosis, two are seen to be nearly twice as long as
the others, but of equal length (figs. 48, 49, 50.) There are 46
chromosomes in the equatorial plate of a spermatogonial spindle (fig.
50). Besides the nucleolus (_n_), there appears in the young
spermatocyte a conspicuous element (_x_) which stains deeply with all
chromatin stains (fig. 51). It is closely applied to the nuclear
membrane and is connected with an end of the spireme (figs. 51-54). At
first it is quite small, and it gradually increases in size during the
spireme stage. There is no "bouquet stage" in this form. Figure 55 shows
the spireme segmented and split longitudinally. The segments have begun
to open out at the center to give the cross which is the typical tetrad
form in _Stenopelmatus_. Figures 56, 58, 59, and 60 show various stages
in the contraction of the split segments to form crosses and
diamond-shaped rings. The tetrads usually remain connected by delicate
linin threads, as shown in figures 57 and 60, also in figures 62 and 63,
the latter taken from the metaphase of the first maturation spindle. If
these linin connections persist, as they appear to do, from the
segmentation of the spireme to metakinesis, the first division of the
contracted tetrads must be longitudinal, corresponding to the split in
the segments of figures 55, 57, 58, etc. The chromosomes in the
metaphase usually appear as dumbbells (fig. 66) or elongated crosses
(fig. 67), but occasionally one can be found which still shows its
tetrad nature (fig. 64), so clearly indicated in the quadrivalent
crosses of figure 59. In the anaphase the chromosomes are often split as
in figure 68, and occasionally the two components can be seen as plainly
as in figure 65. Figure 61 shows the various shapes assumed by the
element _x_ during the tetrad-stage of the chromosomes. This element _x_
almost invariably appears in a vesicle near one pole of the spindle
(figs. 67, 68); in exceptional cases it is found nearer the equatorial
plate, as in figure 66, or even in the same plane with the ordinary
chromosomes, but always somewhat isolated from them. In position